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Technical Service Bulletin
SUBJECT:

TSB−15−54−005

No:

DEW CONDENSATION IN HEADLIGHTS
AND TAILLIGHTS

September, 2015

DATE:
MODEL:

ALL

CIRCULATE TO:

[ ] GENERAL MANAGER

[ X ] PARTS MANAGER

[ X ] TECHNICIAN

[ X ] SERVICE ADVISOR

[ X ] SERVICE MANAGER

[ X ] WARRANTY PROCESSOR

[ ] SALES MANAGER

PURPOSE
Some customers may report moisture or fogging inside headlights or taillights. This condition is typically caused by dew condensation, most often on rainy days or after car washing. The condensation
normally dissipates within one hour after lights are turned on.
This TSB explains the difference between normal dew condensation, which is a natural phenomenon,
and water penetration caused by improper sealing or a defective/broken part.
NOTE: Each reported case should be evaluated thoroughly before replacing a headlight or taillight. Only if normal
condensation is ruled out, and the part is judged to be defective, should a headlight or taillight be replaced.

It may be necessary to explain to the customer:
1. It may not be possible to prevent fogging of a headlight or taillight lens under certain conditions.
2. Dew condensation is generated by differences of temperature, or after vehicle has been exposed to
water (such as rain or washing the car).
3. Humid weather may increase the condensation effect.
4. Condensation should dissipate within one hour after lights have been on.

AFFECTED VEHICLES
All vehicles.

PROCEDURE
If a customer expresses concern related to moisture inside a headlight or taillight, review all the information in this TSB to determine the cause. After reading the entire TSB, determine whether the light
needs to be replaced.
D

If the condensation dissipates after the light has been on for one hour, do NOT replace the light
assembly. Explain to the customer that this is normal dew condensation.

D

If the condition is judged to be water penetration, and the moisture remains in the light after one
hour of the light being on, then the light assembly may need to be replaced.

Dew Condensation vs Water Penetration
The two main causes of a fogged headlight or taillight are dew condensation or water penetration.
Dew condensation is a natural phenomenon and is not a part failure. It typically dissipates within one
hour after lights have been on.
In contrast, water penetration may be caused by a part defect such as improper sealing, where water
drops remain inside and do not dissipate after lights have been on for at least an hour. If water drops
still remain inside the light after one hour, with lights being on, then water penetration can be
suspected.
Copyright 2015, Mitsubishi Motors North America, Inc.

Continued

The information contained in this bulletin is subject to change. For the latest version of this document, go to the Mitsubishi Dealer Link,
MEDIC, or the Mitsubishi Service Information website (www.mitsubishitechinfo.com).
(4289)

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TSB−15−54−005

Dew Condensation vs Water Penetration in Headlight
Water Entry Area

Water Drops Remain

Dew Condensation

Water Penetration (due to improper sealing)

Explanation of Dew Condensation (as a natural phenomenon)
Dew condensation occurs as a natural phenomenon: the inside of a windshield becomes fogged when
driving in rain, and house windows become fogged in winter.
Atmospheric air contains moisture even in fair weather. Higher temperature air can contain a large
amount of moisture, but when the temperature drops, the amount of contained moisture decreases
and the moisture that is left becomes dew condensation. This principle is demonstrated in a fogged
car windshield or windows on a house. The window is heated by the warmer indoor air, which contains
more moisture than the colder air outside. The window is cooled by the colder outside air, which causes the warmer air on the inside of the window to cool, and release moisture in the form of dew condensation.
Dew Condensation/Fogging of Headlights and Taillights
Headlights and taillights become fogged as part of a normal dew condensation process.
When the light is on, it generates heat, and air inside
of the housing expands and contracts as the lights are
turned on and off. The housing of headlights and taillights are designed with breathing holes that allow ambient air to flow into and out of the light housing. This
design helps to prevent cracks and damage to the seal
from pressure fluctuation.
Breathing Holes

When air outside of the light unit is humid, the moisture
enters the light housing through the breathing holes as
the light is turned on and off.

While some of the suctioned moisture dissipates, some of it stays inside the unit. In addition, resin materials of the light itself release moisture into the light unit as temperature rises. This warmer residual
moisture becomes dew condensation when it contacts a cooler lens (for example, a lens that has
been cooled by rain or washing the vehicle).

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TSB−15−54−005

Dew condensation most often occurs in the following conditions:
D

Extreme temperature differences

D

After washing the vehicle

D

Driving in the rain

D

Sunlight hitting the light in cold ambient temperatures (e.g., morning sun in winter)
Cross Section Diagram of Condensation in Headlight

Fast
Cooling

Residual Moisture

Breathing Hole
Outlet &
Inlet Air

Entry of Moisture

Diffusion of Moisture
from Plastic
Fogged (Dew Condensation)

WARRANTY INFORMATION
This bulletin is supplied as technical information only and is not an authorization to repair. If an affected
vehicle is reported with the described condition, diagnose the condition, repair as described in this bulletin
and submit a normal warranty claim using the following information.